More than 280 people, many of them students from the same high school, were missing after a ferry capsized off South Korea on Wednesday, in what could be the country's biggest maritime disaster in over 20 years.

The ferry was carrying 462 people, of whom 174 have been rescued, coastguard officials said. Four people were confirmed dead, but as frantic rescue operations continued late into the night under light from flares, hopes were fading for the 284 unaccounted for.